Crossover Effects in Lithium‐Metal Batteries with a Localized High Concentration Electrolyte and High‐Nickel Cathodes

While crossover effects, such as transition-metal dissolution, are well-understood in lithium-ion batteries, there is a limited understanding of the effect of crossed-over chemical species in cells with oxide cathodes and lithium-metal anodes. In this work, the effects of cathode-to-anode and anode-to-cathode crossover are explored in cells with a high-nickel cathode, lithium-metal anode, and a localized high-concentration electrolyte (LHCE). Dramatic differences are found among cells; a lithium-metal anode paired with a high-nickel cathode has three times less solid-electrolyte interphase growth than a lithium-metal anode paired with lithium metal. Meanwhile, the cathode paired with lithium metal has 2-3 times higher capacity fade than the same cathode paired with graphite. Decomposition and crossover of the FSI salt is identified as the main source of these changes. The fluorine in the salt is first stripped off at the lithium-metal anode, and the remaining sulfur and nitrogen cross over to the cathode. Although the reduction in fluorine content harms the surface stability of the cathode, the lithium-metal anode benefits from the increased fluorine content. Because the lithium-metal anode is typically the bottleneck for cells with thin lithium, crossover is a major factor in the enhanced performance of lithium-metal batteries with LHCE.